The present invention relates to a ball point pen having low-viscosity ink directly reserved in an ink tube, and an ink follower disposed at a rear end of the ink.
In the conventional art, as disclosed in JP-Y2-2555677 (Japanese Registered Utility Model Publication Number: 2555677), a ball point pen has a paste-like backflow preventing agent disposed in an ink tube charged with ink in front of the backflow preventing agent, a tip fixed to a front end of the ink tube while rotatably holding a ball partially protruding from a front end of the tip, and a spring for urging the ball to come into contact with an inward front end edge of the tip when the ball point pen is not used. Further, low-viscosity aqueous ink is charged in the ink tube.
In the conventional-art ball point pen, low-viscosity aqueous ink is charged. Accordingly, abundant ink outflow characteristic can be satisfied when writing starts. There is however the possibility that scratchiness may occur in writing at an early stage after the start of writing because ink outflow characteristic has a tendency to decrease gradually as the head of ink (i.e., water head pressure of ink applied on the pen point) decreases gradually after the start of writing.
To eliminate the scratchiness in writing, it may be conceived that the gap between the inner surface of the front end edge portion and the ball is formed largely in advance. In this case, there is however the possibility that blur may occur in writing because the outflow of ink is too much after the start of writing.
The present invention is developed to solve the problem in the conventional art and an object of the invention is to provide a ball point pen in which there is no possibility of occurrence of scratchiness and blur in writing until almost consumption of charged ink after the start of writing, even though low-viscosity ink is charged in the ball point pen.
The inventor has made eager examination to solve the problem. As a result, it has been found that occurrence of scratchiness and blur in writing can be suppressed when an outflow of ink (i.e., the amount of consumed ink) until almost consumption of charged ink after the start of writing is specified. The inventor has further paid attention to the fact that the decrement of the head of ink and the increase of the gap between the inner surface of the front end edge portion and the ball (i.e., abrasion of the ball seat) are intimately related to the outflow of ink. As a result, it has been found that the outflow of ink until almost consumption of charged ink after the start of writing can be kept in a proper range to suppress occurrence of scratchiness and blur in writing when the decrement of the head of ink and the increase of the gap between the inner surface of the front end edge portion and the ball are specified.
(1) That is, according to a first aspect, the invention provides a ball point pen 1 including: a tip body 2 including a front end edge portion 21 and a ball seat 22 provided inward at a front end, and a ball 3 rotatably held in the front end edge portion 21 and the ball seat 22; an ink tube 6 formed so that the tip body 2 is provided at a front end of the ink tube 6; ink 7 reserved in the ink tube 6; an ink follower 8 disposed at a rear end of the ink 7 and advancing with consumption of the ink 7; and an elastic member 4 for urging the ball 3 forward to bring the ball 3 into close contact with an inner surface of the front end edge portion 21 of the tip body 2, wherein the value of outflow of ink per writing distance of 100 m until a measurement time just before outflow of 80% of the amount of charged ink from the start of writing in the case where an outflow of ink is measured at intervals of a writing distance of 100 m is selected to be in a range between a value smaller by 20 mg than the outflow of ink in the writing distance range of from 0 m to 100 m and a value larger by 20 mg than the outflow of ink in the writing distance range of from 0 m to 100 m.
According to the first aspect, the outflow of ink until almost consumption of charged ink after the start of writing can be kept in a proper range to thereby suppress occurrence of scratchiness and blur in writing.
If the outflow of ink per writing distance of 100 m is smaller than a value smaller by 20 mg than the outflow of ink in the writing distance range of from 0 m to 100 m, there is the possibility that scratchiness may occur in writing because the outflow of ink decreases remarkably compared with that at the time of the start of writing. On the contrary, if the outflow of ink per writing distance of 100 m is larger than a value larger by 20 mg than the outflow of ink in the writing distance range of from 0 m to 100 m, there is the possibility that blur may occur in writing because the outflow of ink increases remarkably compared with that at the time of the start of writing.
The phrase xe2x80x9ca measurement time just before outflow of 80% of the amount of charged ink from the start of writing in the case where an outflow of ink is measured at intervals of a writing distance of 100 mxe2x80x9d is used for specifying the writing distance in the case where almost of charged ink is consumed.
The writing distance range in the case where almost of charged ink is consumed may be more preferably set xe2x80x9ca measurement time just after outflow of 80% of the amount of charged ink from the start of writing in the case where an outflow of ink is measured at intervals of a writing distance of 100 mxe2x80x9d in order to elongate the writing-enabled distance in which the outflow of ink can be kept in a proper range.
(2) Preferably, in a second aspect, in addition to the first aspect, in the ball point pen according to the invention, the decrement xcex94H of the head of ink per writing distance of 100 m until a measurement time just before outflow of 80% of the amount of charged ink from the start of writing in the case where an outflow of ink is measured at intervals of a writing distance of 100m is selected to be in a range of from 3 mm to 12 mm.
According to the second aspect, occurrence of scratchiness and blur in writing can be surely prevented until almost of charged ink is consumed after the start of writing.
If the decrement xcex94H of the ink head per writing distance of 100 m is smaller than 3 mm, there is the possibility that scratchiness may occur in writing easily because the outflow of ink from the front end of the tip body 2 is too little. On the contrary, if the decrement xcex94H of the ink head per writing distance of 100 m is larger than 12 mm, there is the possibility that blur may occur in writing easily because the outflow of ink from the front end of the tip body 2 is too much.
The phrase xe2x80x9cthe decrement xcex94H of the ink head per writing distance of 100 mxe2x80x9d means an average of descending speed of the ink head due to writing in a time range of from the start of writing to a measurement time just before consumption of 80% of the amount of charged ink in the case where an outflow of ink is measured at intervals of a writing distance of 100 m. The term xe2x80x9cink headxe2x80x9d used herein means a height (mm) of the rear end of ink from the pen point when the ball point pen is placed with the pen point down.
(3) Preferably, in a third aspect, in addition to the second aspect, in the ball point pen 1 according to the invention, the increment xcex94C of longitudinal movable length C of the ball 3 at a front end of the tip body 2 per writing distance of 100 m until a measurement time just before outflow of 80% of the amount of charged ink from the start of writing in the case where an outflow of ink is measured at intervals of a writing distance of 100 m is selected to be in a range of from 0.1 xcexcm (0.0001 mm) to 1.5 xcexcm (0.0015 mm) (more preferably in a range of from 0.1 xcexcm to 1.0 xcexcm, further preferably in a range of from 0.1 xcexcm to 0.5 xcexcm).
According to (3), the outflow of ink can be more surely set in a proper range until almost of charged ink is consumed after the start of writing, so that occurrence of scratchiness and blur in writing can be prevented.
If the increment xcex94C of longitudinal movable length C of the ball 3 at the front end of the tip body 2 per writing distance of 100 m is smaller than 0.1 xcexcm, the outflow of ink cannot be kept constant because the increment of the gap between the ball 3 and the inner surface of the front end edge portion 21 due to writing is excessively small so that the outflow of ink decreases gradually according to writing with the decrement of the ink head due to writing.
On the contrary, if the increment xcex94C of longitudinal movable length C of the ball 3 at the front end of the tip body 2 per writing distance of 100 m is larger than 1.5 xcexcm, the outflow of ink cannot be kept constant because the increment of the gap between the ball 3 and the inner surface of the front end edge portion 21 due to writing is excessively large so that the outflow of ink increases gradually according to writing to overcome the function of decreasing the ink head due to writing.
That is, in the ball point pen 1 as in (3), the function of gradually decreasing the outflow of ink due to the descending of the ink head and the function of gradually increasing the outflow of ink due to the abrasion of the ball seat 22 are balanced with each other so that the outflow of ink can be kept approximately constant.
The phrase xe2x80x9cthe increment xcex94C of longitudinal movable length C of the ball 3 at the front end of the tip body 2 per writing distance of 100 mxe2x80x9d means an average of increasing speed of the gap between the ball 3 and the inner surface of the front end edge portion 21 (i.e., abrading speed of the ball seat 22 due to writing).
(4) Preferably, in a forth aspect, in addition to the afore mentioned aspects, in the ball point pen 1 according to the invention, the viscosity of the ink 7 at 20xc2x0 C. is selected to be in a range of from 1 mPa.s to 50 mPa.s.
According to (4), because the viscosity of the ink 7 is low, ink follow-up characteristic is improved so that smooth writing can be made without scratchiness in writing even in the case where writing is made at a high speed.
(5) Preferably, in a fifth aspect, in addition to one of first to third aspects, in the ball point pen 1 according to the invention, the viscosity of the ink 7 measured at 20xc2x0 C. at a rotational speed of 100 rpm by an E-type rotational viscometer is selected to be in a range of from 3 mpa.s to 160 mPa.s, and the shear-thinning index of the ink 7 is selected to be in a range of from 0.80 to 0.99.
According to (5), because the viscosity of the ink 7 is low, ink follow-up characteristic is improved so that smooth writing can be made without scratchiness in writing even in the case where writing is made at a high speed.
Incidentally, the shear-thinning index n is a value calculated according to an experimental equation T=Kjn (in which K is a constant calculated) derived by rheological measurement of shear stress (T) and shear rate (j) with a viscometer. Incidentally, specific examples of the E-type rotational viscometer include an EM-type rotational viscometer, an EL-type rotational viscometer, and an EH-type rotational viscometer.